In accordance with an embodiment, a stopping circuit includes a detection circuit connected to a subtraction amount determination circuit. A subtraction circuit is connected to the subtraction circuit and the subtraction circuit is coupled for receiving an output signal from the subtraction amount determination circuit. A duty determination is connected to the subtraction circuit and a state controller is connected to the duty determination circuit. A counter is connected to a state controller. In accordance with another embodiment a method for stopping a motor is provided by decreasing a duty of a drive signal. The duty of the drive signal is lowered from a first level to a predetermined level. A braking state is entered in response to the duty of the pulse width modulation signal achieving the predetermined level.
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10. A method for stopping a motor, comprising:
providing a drive circuit configured to drive the motor;
providing a drive signal that has a duty at a first level, wherein the drive signal is configured to drive the motor;
reducing the duty of the drive signal from the first level in response to a pulse width modulation (pwm) OFF signal that indicates that an input pwm signal is off; and
entering a braking state in response to the duty of the drive signal achieving a predetermined level which includes turning off a first transistor;
in response to the motor stopping, performing high impedance processing including turning off a second transistor.
1. A method for stopping a motor, comprising:
in response to an input pulse width modulation signal being off, generating a pulse width modulation off signal;
decreasing a duty of a drive signal to a driver circuit;
in response to the pulse width modulation off signal;
comparing the duty of the drive signal with a predetermined level;
in response to the duty of the drive signal being greater than the predetermined level, continue decreasing the duty of the drive signal;
in response to the duty of the drive signal being less than or equal to the predetermined level, entering a braking state which includes turning off a first transistor; and
in response to the motor stopping, performing high impedance processing including turning off a second transistor.
2. The method of
3. The method of
4. The method of
5. The method of
determining an amount to decrease the duty of the drive signal; and
adjusting the duty of drive signal using the amount to decrease the duty of the drive signal.
6. The method of
7. The method of
generating a signal in response to an output signal of a Hall sensor;
determining a period of the signal generated in response to the output signal of the Hall sensor; and
entering a high impedance state in response to the period of the signal generated in response to the output signal of the Hall sensor being greater than a predetermined value.
9. The method of
12. The method of
13. The method of
15. The method of
16. The method of
providing a first pair of transistors comprising a first transistor coupled to a second transistor;
providing a second pair of transistors comprising a third transistor coupled to a fourth transistor;
providing a third pair of transistors comprising a fifth transistor coupled to a sixth transistor; and wherein
entering the high impedance state includes turning off a plurality of transistors; and wherein
entering the braking state includes turning off one transistor of the first pair of transistors, one transistor of the second pair of transistors, and one transistor of the third pair of transistors.
17. The method of
18. The method of
19. The method of
generating a sensing signal in response to a signal from the sensing device, the sensing signal having a period;
determining that the motor is stopped in response to the period of the sensing signal being greater than a predetermined period.
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The present invention relates, in general, to motors and, more particularly, to three phase motors.
Multi-phase motors are used in a variety of applications including disc drives, digital video disc players, scanners, printers, plotters, actuators used in automotive and aviation industries, etc. Generally, multiple phase motors include a stationary portion or stator that produces a rotating magnetic field and a non-stationary portion or rotor in which torque is created by the rotating magnetic field. The torque causes the rotor to rotate which in turn causes a shaft connected to the rotor to rotate. The motors are driven by motor drive circuits.
Motor drive circuits are designed to meet desired motor performance parameters which may include noise level specifications, start-up specifications, maximum rotational speed specifications, etc. Noise specifications may be set to provide continuity of current flow during motor startup, or during motor rotation, or during motor stoppage. Start-up or motive power specifications may be set so that the motor reliably starts. Rotational speed specifications may be set to ensure there is sufficient torque drive to cover a large number of different motors. For example, the desired rotational speed of a server is higher than that of a personal computer. It is commonly believed that three-phase motors are better at achieving the desired specifications compared to single phase motors; however, three-phase motors cost more than single phase motors. In addition, three-phase motors provide current having sinusoidal characteristics from motor start-up to motor stoppage or cessation and they allow accurate determination of motor position and rotation speed. Three-phase motors typically include three Hall sensors, which is one of the reasons these motors are more expensive to manufacture. A Hall sensor may be referred to as a Hall element. U.S. Pat. No. 6,359,406 issued to Hsien-Lin Chiu et al. on Mar. 19, 2002, discloses three-phase motors and in particular discloses a three-phase motor having two Hall sensors or two Hall elements. A drawback with this technology is that it uses special bias circuitry that complicates its design and increases costs. A technique to lower the cost of three-phase motors is to manufacture the motor drive circuitry as a sensorless motor drive circuit, i.e., a motor without sensors. U.S. Pat. No. 6,570,351 issued to Shinichi Miyazaki et al. on May 27, 2003, discloses a three-phase motor without sensors. A drawback with sensor-less motor drive configurations is that they may fail to start if the inductive voltage of the coil is small. Another drawback is that stopping procedures for the motor typically include rapidly shutting off the output pulse width modulation signal which creates large fluctuations in coil current and can generate a revving sound from the motor. This noise is particularly noticeable during low speed rotation.
Accordingly, it would be advantageous to have a multi-phase motor drive circuit and a method for driving the motor configured to reduce noise during a stopping procedure. It is desirable for the multi-phase drive circuit and method to be cost and time efficient to implement.
The present invention will be better understood from a reading of the following detailed description, taken in conjunction with the accompanying drawing figures, in which like reference characters designate like elements and in which:
For simplicity and clarity of illustration, elements in the figures are not necessarily to scale, and the same reference characters in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or an anode of a diode, and a control electrode means an element of the device that controls current flow through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain n-channel or p-channel devices, or certain n-type or p-type doped regions, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with embodiments of the present invention. It will be appreciated by those skilled in the art that the words during, while, and when as used herein are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay, such as a propagation delay, between the reaction that is initiated by the initial action and the initial action. The use of the words approximately, about, or substantially means that a value of an element has a parameter that is expected to be very close to a stated value or position. However, as is well known in the art there are always minor variances that prevent the values or positions from being exactly as stated. It is well established in the art that variances of up to about ten percent (10%) (and up to twenty percent (20%) for semiconductor doping concentrations) are regarded as reasonable variances from the ideal goal of exactly as described.
It should be noted that a logic zero voltage level (VL) is also referred to as a logic low voltage or logic low voltage level and that the voltage level of a logic zero voltage is a function of the power supply voltage and the type of logic family. For example, in a Complementary Metal Oxide Semiconductor (CMOS) logic family a logic zero voltage may be thirty percent of the power supply voltage level. In a five volt Transistor-Transistor Logic (TTL) system a logic zero voltage level may be about 0.8 volts, whereas for a five volt CMOS system, the logic zero voltage level may be about 1.5 volts. A logic one voltage level (VH) is also referred to as a logic high voltage level, a logic high voltage, or a logic one voltage and, like the logic zero voltage level, the logic high voltage level also may be a function of the power supply and the type of logic family. For example, in a CMOS system a logic one voltage may be about seventy percent of the power supply voltage level. In a five volt TTL system a logic one voltage may be about 2.4 volts, whereas for a five volt CMOS system, the logic one voltage may be about 3.5 volts.
The present description includes, among other features, a motor drive circuit and a method for driving a motor that includes a stopping circuit configured to decrease a duty of a drive signal to a predetermined level such as, for example, 0%, while maintaining rotor rotation when arriving at the predetermined duty level. The stopping circuit enters a short brake state in which the rotor slowly stops. Then the stopping circuit places the drive transistors in a high impedance state.
In accordance with an embodiment, a method for stopping a motor includes providing a pulse width modulation signal having a duty at a first level then decreasing the duty of the pulse width modulation signal from the first level to a predetermined level. A braking state is entered in response to the duty of the pulse width modulation signal achieving the predetermined level.
In accordance with an aspect, a stopping motor determines if the motor has stopped after entering the braking state.
In accordance with another aspect, the predetermined level ranges from about 10% to about 0%.
In accordance with another aspect, decreasing the duty of the pulse width modulation signal comprises determining an amount to decrease the duty of the pulse width modulation signal and adjusting the duty of the pulse width modulation signal using the amount to decrease the duty of the pulse width modulation signal.
In accordance with another aspect, decreasing the duty of the pulse width modulation signal further includes comparing the duty with the predetermined level and in response to the duty being greater than the predetermined level continuing to decrease the duty.
In accordance with another aspect, a stopping circuit generates a signal in response to an output signal of a Hall sensor, determines a period of the signal generated in response to the output signal of the Hall sensor, and enters a high impedance state in response to the period of the signal generated in response to the output signal of the Hall sensor being greater than a predetermined value.
In accordance with another aspect, the method for stopping the motor applies to a fan motor.
In accordance with another aspect, the drive transistors enter into a high impedance state in response to the motor being stopped.
In accordance with another embodiment, a method for stopping a motor comprises providing a motor having a rotor, a stator, and a plurality of coils and coupling a sensing device and a drive circuit to the motor. A duty of a drive signal that drives the motor is provided wherein the duty is at a first level. Alternatively, the duty of the drive signal may be determined. The duty of the drive signal is reduced from the first level in response to a pulse width modulation (PWM) OFF signal indicating that an input PWM signal is off. The motor enters a braking state in response to the duty of the drive signal achieving a predetermined level.
In accordance with an aspect, reducing the duty of the drive signal includes linearly reducing the duty of the drive signal.
In accordance with another aspect, first, second, and third pairs of transistors are provided wherein the first pair of transistors comprises a first transistor coupled to a second transistor; the second pair of transistors comprises a third transistor coupled to a fourth transistor; and the third pair of transistors comprises a fifth transistor coupled to a sixth transistor. In addition, entering the high impedance state includes turning off a plurality of transistors; and entering the braking state includes turning off one transistor of the first pair of transistors, one transistor of the second pair of transistors, and one transistor of the third pair of transistors.
In accordance with another aspect, the high impedance state is entered in response to the motor being stopped.
In accordance with another aspect, entering the high impedance state includes turning off the transistors of the first, second, and third pairs of transistors that are on.
In accordance with another embodiment, the stopping circuit, comprises a detection circuit connected to a subtraction amount determination circuit. A subtraction circuit is connected to the subtraction amount determination circuit and a duty determination circuit is connected to the subtraction circuit. A state controller has an input connected to an output of the duty determination circuit and another input connected to a counter.
Rotational state generation circuit 54 has inputs 80 and 82, an input/output 84, and may be referred to as an FG generation circuit. Output 78 of FG signal masking circuit 52 is connected to input 80 of FG generation circuit 54. Input/output 84 may be referred to as an input/output node, an I/O node, an input/output terminal, an I/O terminal, or the like. Rotational state generation circuit 54 may be comprised of a control circuit 86 coupled to a multiplier circuit 88. It should be noted that input 80 and input 84 are connected to multiplier control circuit 86 and input/output 84 is connected to multiplier circuit 88. PWM detection circuit 56 has an output connected to an input of state controller 60 and to an input of duty control controller 62 and is configured to determine the speed of rotor 18. It should be noted that if the duty range is small the speed of the rotor is smaller than if the duty range is large. Timer 58 has an output connected to input 82 of rotational state generation circuit 54 and to an input 92 of state controller 60 and may include a timer counter 90. In addition, state controller 60 has an input/output 94 connected to an input/output 84 of rotational state generation circuit 54, an input 98 connected to output 78 of FG signal masking circuit 52, and an input/output 96 connected to an input/output 100 of duty control controller 62. By way of example, duty control controller 62 is comprised of a calculation device 102 configured to determine an amount of change to the duty cycle, a summer 104, and a PWM converter 106. Calculation device 102 has an input that serves as input/output 100 and an output connected to an input of summer 104. In addition, summer 104 has an output that is connected to an input of PWM output converter 106 and to another input of summer 104. An output 108 of PWM output converter 106 serves as an output of duty control controller 62. State controller 60 is configured for determining the status or condition of the FG signal and the PWM signal and duty control controller 62 is configured to control an output sine wave, which helps to make the motor quieter.
Output duty generation circuit 64 has an input 110 connected to an output 99 of output of state controller 60, an input 112 connected to output 108 of output duty generation circuit 62, and a plurality of outputs 114, 116, and 118 connected to corresponding inputs of drive control signal generation circuit 66, which signal generation circuit 66 has a plurality of outputs 120, 122, and 124 connected to corresponding inputs of output drive stage 68. In accordance with an embodiment, drive stage 68 includes driver devices 126, 128, and 130 having inputs that serve as inputs 126A, 128A, and 130A of output drive stage 68, a pair 66A of transistors having a terminal connected to U-phase winding 24, a pair 66B of transistors having a terminal connected to W-phase winding 26, and a pair 66C of transistors having a terminal connected to V-phase winding 28. Pair of transistors 66A is comprised of transistors 66A1 and 66A2, wherein each transistor has a control electrode, and a pair of current carrying electrodes. The control electrodes of transistors 66A1 and 66A2 are coupled for receiving control signals from driver device 126, one current carrying electrode of transistor 66A1 is coupled for receiving a source of potential VDD and the other current carrying electrode of transistor 66A1 is connected to a current carrying electrode of transistor 66A2. The other current carrying terminal of transistor 66A2 is coupled for receiving a source of potential VSS such as, for example, a ground potential. The commonly connected current carrying electrodes of transistors 66A1 and 66A2 are connected to U-phase winding 24.
Pair of transistors 66B is comprised of transistors 66B1 and 66B2, wherein each transistor has a control electrode, and a pair of current carrying electrodes. The control electrodes of transistors 66B1 and 66B2 are coupled for receiving control signals from driver device 128, one current carrying electrode of transistor 66B1 is coupled for receiving a source of potential VDD and the other current carrying electrode of transistor 66B1 is connected to a current carrying electrode of transistor 66B2. The other current carrying terminal of transistor 66B2 is coupled for receiving a source of operating potential VSS such as, for example, a ground potential. The commonly connected current carrying electrodes of transistors 66B1 and 66B2 are connected to U-phase winding 26.
Pair of transistors 66C is comprised of transistors 66C1 and 66C2, wherein each transistor has a control electrode, and a pair of current carrying electrodes. The control electrodes of transistors 66C1 and 66C2 are coupled for receiving control signals from driver device 130, one current carrying electrode of transistor 66C1 is coupled for receiving a source of potential VDD and the other current carrying electrode of transistor 66C1 is connected to a current carrying electrode of transistor 66C2. The other current carrying terminal of transistor 66C2 is coupled for receiving a source of operating potential VSS such as, for example, a ground potential. The commonly connected current carrying electrodes of transistors 66C1 and 66C2 are connected to U-phase winding 28.
A comparator 136 has inputs connected to corresponding inputs of a Hall sensor 14 and an output 138 connected to input 76 of rotational state generation circuit 54.
It should be noted that in accordance with an alternative embodiment, FG signal masking circuit 52 is absent from drive circuit 12 and that output 138 of comparator 136 is commonly connected to input 76 of rotational state generation circuit 54 and to input 98 of state controller 60.
In accordance with an embodiment, an output duty gradually decreases for a specific period of time and the motor shuts off in response to passage of a predetermined period of time after a rotation signal is no longer detected.
In accordance with an embodiment, a control circuit controls a motor which has a rotor with a magnetic pole, a three-phase stator with an exciting coil and a single Hall element used for detecting position of the rotor.
In accordance with another embodiment, the output pulse width modulation (PWM) signal ceases gradually upon termination of an input PWM, where the output PWM signal gradually decreases with a change ratio in a sine wave-like fashion over a predetermined period of time. Thus, the output PWM gradually stops or has a ceased status.
Counter 210 has an input coupled for receiving a rotation indicator signal VFG and an output 210B connected to an input 60B of state controller 60. State controller 60 has an output 60C through which a PWM OFF order signal is transmitted indicating the order in which the drive transistor pairs are turned off and an output 60D through which a braking order is indicated.
If the duty of the drive signal is less than or equal to the predetermined duty, i.e., the duty of the drive signal has achieved a predetermined level, stopping circuit 200 enters a short braking state (indicated by box 238). In accordance with an embodiment, during the short braking state stopping circuit 200 turns off p-channel transistors 66A1, 66B1, and 66C1 (shown in
Counter 210 counts the oscillations of the output signal generated in response to the output signal from Hall sensor 14 to determine the period of the Hall sensor output signal. It should be noted that the output signal of comparator 136 that is generated in response to the output signal from Hall Sensor 14 may be referred to as an FG signal VFG. Stopping circuit 200 determines whether motor 10 has stopped as indicated by decision diamond 240. By way of example, motor stoppage may be indicated by the period of the FG signal VFG exceeding a pre-set period or a predetermined period. If the period of FG signal VFG is less than the predetermined period, then stopping circuit 200 remains in the braking state (indicated by the NO branch of decision diamond 240). If the period of signal VFG is greater than the predetermined period then counter 210 sends a stop detection signal to state controller 60 and stopping circuit 200 performs high impedance processing (indicated by the YES branch of decision diamond 240 and box 242). In response to performing high impedance processing, stopping circuit 200 turns off n-channel transistors 66A2, 66B2, and 66C2, thereby placing transistors 66A1, 66B1, 66C1, 66A2, 66B2, and 66C2 in a high impedance state. Stopping circuit 200 terminates the stopping process (indicated by box 244).
Although specific embodiments have been disclosed herein, it is not intended that the invention be limited to the disclosed embodiments. Those skilled in the art will recognize that modifications and variations can be made without departing from the spirit of the invention. It is intended that the invention encompass all such modifications and variations as fall within the scope of the appended claims.
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